// ASM: a very small and fast Java bytecode manipulation framework
// Copyright (c) 2000-2011 INRIA, France Telecom
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package org.objectweb.asm;

/**
 * The path to a type argument, wildcard bound, array element type, or static inner type within an enclosing type.
 *
 * @author Eric Bruneton
 */
public final class TypePath {

	/** A type path step that steps into the element type of an array type. See {@link #getStep}. */
	public static final int ARRAY_ELEMENT = 0;

	/** A type path step that steps into the nested type of a class type. See {@link #getStep}. */
	public static final int INNER_TYPE = 1;

	/** A type path step that steps into the bound of a wildcard type. See {@link #getStep}. */
	public static final int WILDCARD_BOUND = 2;

	/** A type path step that steps into a type argument of a generic type. See {@link #getStep}. */
	public static final int TYPE_ARGUMENT = 3;

	/**
	 * The byte array where the 'type_path' structure - as defined in the Java Virtual Machine Specification (JVMS) - corresponding to this TypePath is stored. The first byte of the structure in this array is given by {@link #typePathOffset}.
	 *
	 * @see <a href="https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7.20.2">JVMS 4.7.20.2</a>
	 */
	private final byte[] typePathContainer;

	/** The offset of the first byte of the type_path JVMS structure in {@link #typePathContainer}. */
	private final int typePathOffset;

	/**
	 * Constructs a new TypePath.
	 *
	 * @param typePathContainer
	 *          a byte array containing a type_path JVMS structure.
	 * @param typePathOffset
	 *          the offset of the first byte of the type_path structure in typePathContainer.
	 */
	TypePath(final byte[] typePathContainer, final int typePathOffset) {
		this.typePathContainer = typePathContainer;
		this.typePathOffset = typePathOffset;
	}

	/**
	 * Returns the length of this path, i.e. its number of steps.
	 *
	 * @return the length of this path.
	 */
	public int getLength() {
		// path_length is stored in the first byte of a type_path.
		return typePathContainer[typePathOffset];
	}

	/**
	 * Returns the value of the given step of this path.
	 *
	 * @param index
	 *          an index between 0 and {@link #getLength()}, exclusive.
	 * @return one of {@link #ARRAY_ELEMENT}, {@link #INNER_TYPE}, {@link #WILDCARD_BOUND}, or {@link #TYPE_ARGUMENT}.
	 */
	public int getStep(final int index) {
		// Returns the type_path_kind of the path element of the given index.
		return typePathContainer[typePathOffset + 2 * index + 1];
	}

	/**
	 * Returns the index of the type argument that the given step is stepping into. This method should only be used for steps whose value is {@link #TYPE_ARGUMENT}.
	 *
	 * @param index
	 *          an index between 0 and {@link #getLength()}, exclusive.
	 * @return the index of the type argument that the given step is stepping into.
	 */
	public int getStepArgument(final int index) {
		// Returns the type_argument_index of the path element of the given index.
		return typePathContainer[typePathOffset + 2 * index + 2];
	}

	/**
	 * Converts a type path in string form, in the format used by {@link #toString()}, into a TypePath object.
	 *
	 * @param typePath
	 *          a type path in string form, in the format used by {@link #toString()}. May be {@literal null} or empty.
	 * @return the corresponding TypePath object, or {@literal null} if the path is empty.
	 */
	public static TypePath fromString(final String typePath) {
		if (typePath == null || typePath.length() == 0) {
			return null;
		}
		int typePathLength = typePath.length();
		ByteVector output = new ByteVector(typePathLength);
		output.putByte(0);
		int typePathIndex = 0;
		while (typePathIndex < typePathLength) {
			char c = typePath.charAt(typePathIndex++);
			if (c == '[') {
				output.put11(ARRAY_ELEMENT, 0);
			} else if (c == '.') {
				output.put11(INNER_TYPE, 0);
			} else if (c == '*') {
				output.put11(WILDCARD_BOUND, 0);
			} else if (c >= '0' && c <= '9') {
				int typeArg = c - '0';
				while (typePathIndex < typePathLength) {
					c = typePath.charAt(typePathIndex++);
					if (c >= '0' && c <= '9') {
						typeArg = typeArg * 10 + c - '0';
					} else if (c == ';') {
						break;
					} else {
						throw new IllegalArgumentException();
					}
				}
				output.put11(TYPE_ARGUMENT, typeArg);
			} else {
				throw new IllegalArgumentException();
			}
		}
		output.data[0] = (byte) (output.length / 2);
		return new TypePath(output.data, 0);
	}

	/**
	 * Returns a string representation of this type path. {@link #ARRAY_ELEMENT} steps are represented with '[', {@link #INNER_TYPE} steps with '.', {@link #WILDCARD_BOUND} steps with '*' and {@link #TYPE_ARGUMENT} steps with their type argument index in decimal form followed by ';'.
	 */
	@Override
	public String toString() {
		int length = getLength();
		StringBuilder result = new StringBuilder(length * 2);
		for (int i = 0; i < length; ++i) {
			switch (getStep(i)) {
			case ARRAY_ELEMENT:
				result.append('[');
				break;
			case INNER_TYPE:
				result.append('.');
				break;
			case WILDCARD_BOUND:
				result.append('*');
				break;
			case TYPE_ARGUMENT:
				result.append(getStepArgument(i)).append(';');
				break;
			default:
				throw new AssertionError();
			}
		}
		return result.toString();
	}

	/**
	 * Puts the type_path JVMS structure corresponding to the given TypePath into the given ByteVector.
	 *
	 * @param typePath
	 *          a TypePath instance, or {@literal null} for empty paths.
	 * @param output
	 *          where the type path must be put.
	 */
	static void put(final TypePath typePath, final ByteVector output) {
		if (typePath == null) {
			output.putByte(0);
		} else {
			int length = typePath.typePathContainer[typePath.typePathOffset] * 2 + 1;
			output.putByteArray(typePath.typePathContainer, typePath.typePathOffset, length);
		}
	}
}
